1. Field of the Invention
The present invention relates to a method of producing a spark plug and a spark plug produced by the same, and more particularly to the method of producing a spark plug that has a high dimensional accuracy in the spark gap.
2. Description of the Related Art
Some of internal combustion engines are of a type that uses spark plugs for igniting air/fuel mixture compressed in combustion chambers of the engine with the aid of electric power.
As is shown in Japanese Laid-open Patent Application (tokkai) 2003-229231 and Japanese Patent 3273215, some of the spark plugs widely used are of a type that includes a center electrode that carries a high-voltage current from an ignition coil and a ground electrode that is located beside the center electrode and bent inward to produce a spark gap between the bent top of the ground electrode and a top of the center electrode. That is, upon application of the high-voltage current to the center electrode, a spark jumps from the center electrode to the ground electrode, which ignites the compressed air/fuel mixture.
For improving the spark, some of known ground electrodes are equipped with a noble metal tip. For producing such spark plugs, one method is known. That is, in the known method, a separate ground electrode is prepared, then a noble metal tip is welded to a leading part of the ground electrode, then the ground electrode thus equipped with the noble metal tip is subjected to a bending process for providing a bent front portion, and then the ground electrode thus bent is secured to a metal shell of the spark plug.